1. Field of the Invention
The present invention generally relates to the art of configuration management and fault detection in modular electrical systems, and more particularly to permitting alternate voltage sources to be applied to daughterboards without conflicts from primary systems that may apply a voltage.
2. Description of the Related Art
Enterprise server systems usually have external input/output (I/O) devices for expansion. The most common expansion bus interface used for this is Peripheral Component Interconnect (PCI) and its extended and improved version PCI-X. When a system supports hot plug capabilities, power to the PCI slots is controlled by hot plug controller modules, hereinafter “hotplug controller”, that are capable of detecting voltage faults and disabling the slot if a fault is found. There are cases where anomalous or false power faults can be detected if a voltage is found in the lines going to the PCI slot prior to the motherboard or system planar powering on. The anomalous fault may happen if an external device connected to the PCI adapter or card is powered on before the motherboard finishes an initial program load. This often happens in the case where external devices are shared between different server systems.
A problem may develop if the external device is powered on before the PCI slots are powered on. No problem develops if the external device is powered on after the PCI slots have been powered-on. However an anomalous fault often occurs if the timing is reversed. That is, the fault is based merely on the timing of applying power, and not on any real defect in the card or supporting system. The problem results in a person performing a manual hotplug operation when the anomalous power fault occurs. Only then, is a person able to properly configure the PCI slot for the system. Otherwise, the PCI slot remains in an unconfigured or disabled state.
A previous solution for the problem was to add extra hardware, such as diodes, inverters or other devices, to prevent current back flow into the PCI slots from the card. Unfortunately, this solution is either not effective or too expensive in situations where a power feedback problem is discovered in motherboards that are already in use in the field. Moreover, additional hardware means greater expenses in assembly, inventory and other costs of production for those motherboards that are intended to be made.
Thus, it would be advantageous if a series of steps or inexpensive apparatus could identify an anomalous power fault and assure that the affected slot is configured or otherwise enabled.